Solid-State Image Pickup Device and Method of Manufacturing Same

ABSTRACT

Disclosed herein is a solid-state image pickup device including: a photoelectric conversion section configured to convert incident light into a signal charge; a transfer transistor configured to read the signal charge from the photoelectric conversion section and transfer the signal charge; and an amplifying transistor configured to amplify the signal charge read by the transfer transistor, wherein a compressive stress film having a compressive stress is formed on the amplifying transistor.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/176,347, filed on Feb. 10, 2014, which is a continuation of U.S.patent application Ser. No. 13/335,030 filed on Dec. 22, 2011, now U.S.Pat. No. 8,691,637 issued on Apr. 8, 2014 which is a division of U.S.patent application Ser. No. 12/372,857, filed Feb. 18, 2009, now U.S.Pat. No. 8,120,684 issued on Feb. 21, 2012 which contains subject matterrelated to Japanese Patent Application JP 2008-054560 filed in the JapanPatent Office on Mar. 5, 2008, the entire contents of which beingincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state image pickup device and amethod of manufacturing the same.

2. Description of the Related Art

With recent increase in degree of integration of semiconductor elements,solid-state image pickup devices have also been increased in the numberof pixels and advanced in miniaturization.

On the other hand, characteristic degradation attendant thereon isbecoming a great problem.

For example, an SN ratio is important for the improvement of imagequality. Specifically, as the miniaturization progresses, a decrease ofphotons that can be taken in due to the miniaturization of a photodiode(PD) as a photoelectric conversion element inevitably reduces a signalquantity. It is thus necessary to improve the SN ratio by reducingnoise.

In CMOS (Complementary Metal Oxide Semiconductor) image sensors, inparticular, as shown in FIG. 14, a charge obtained by photoelectricconversion in a photodiode 221 is accumulated in a floating diffusion226 via a transfer transistor 222 and thereafter subjected to signalamplification in an amplifying transistor 224 in many cases.

A noise proportional to a frequency generated in the amplifyingtransistor 224, or 1/f noise, is dominant as random noise of a pixel,and it is important to suppress the noise. In general, the followingrelation holds for the 1/f noise.

i _(n) ² =KF((Id ^(AF))/(C _(ox) WL _(eff) f ^(EF)))   (1)

where i_(n) ² is drain current noise density [A²/Hz], KF (flicker noisecoefficient) is a factor dependent on the element, Id is a draincurrent, C_(ox) is a gate capacitance per unit area, and L_(eff) is aneffective gate length.

This is disclosed in IEEE Transaction on Electron Devices, Vol. 48, No.5, May 2001, pp. 921 to 927.

According to the above Equation (1), a reduction of line width of theamplifying transistor 224, that is, miniaturization of the amplifyingtransistor 224 sharply increases the noise. KF is a factor dependent onthe amplifying transistor 224, and is greatly affected by processfactors.

One of the process factors is a stress applied to a channel part of theamplifying transistor 224. For higher speed and lower power consumptionof a minute pixel, reducing gate wiring resistance and contactresistance by applying silicide to transistors within a pixel region isa very effective means, and the amplifying transistor 224 is noexception.

Generally, silicide techniques have been introduced to a generation of0.25 μm or later in CMOS logic.

While a pixel region in a CMOS image sensor is highly likely to operateas a device as long as ohmic characteristics are maintained, techniquesfor reducing resistance such as salicide formation or the like becomenecessary with a reduction of a contact diameter.

However, a local tensile stress occurs in a channel part of a fineamplifying transistor where salicide is formed.

In addition, a correlation is found between stress and 1/f noise. Theapplication of tensile stress increases the 1/f noise regardless ofwhether a carrier species is electrons or holes, or in both cases of anN-MOS and a P-MOS (see Authored by T. Ohguro, Y. Okayama, K. Matsuzawa,K. Matsunaga, N. Aoki, K. Kojima, H. S. Momose, and K. Ishimaru, Theimpact of oxynitride process, deuterium annealing and STI stress to 1/fnoise of 0.11 CMOS″ 2003 Symposium on VLSI Technology Digest ofTechnical Papers, 2003, p. 37 and Authored by Shigenobu Maeda, You-SeungJin, Jung-A Choi, Sun-Young Oh, Hyun-Woo Lee, Jae-Yoon Yoo, Min-ChulSun, Ja-Hum Ku, Kwon Lee, Su-Gon Bae, Sung-Gun Kang, Jeong-Hwan Yang,Young-Wug Kim, and Kwang-Pyuk Suh, “Impact of Mechanical StressEngineering on Flicker Noise Characteristics” 2004 Symposium on VLSITechnology Digest of Technical Papers, 2004, pp. 102 to 103, forexample).

For the above-described reasons, when pixels are miniaturized andsalicide is introduced into the pixels, it is difficult to toleratenoise degradation when a high SN ratio is to be achieved.

A process of manufacturing a CMOS image sensor in related art will nextbe described with reference to FIGS. 15A to 15E.

As shown in FIG. 15A, a P-type well region 212 is formed in an N-typesilicon substrate 211.

Next, a photodiode 221 for performing photoelectric conversion is formedat a predetermined position on the surface side of the silicon substrate211. The photodiode 221 is formed by a P-type region, an N-type region,and a P-type region from a bottom layer by performing ion implantationof phosphorus (P) as an N-type impurity and boron (B) as a P-typeimpurity using an ion implantation mask formed by patterning a resistfilm formed on the silicon substrate 211.

The energy of the ion implantation is adjusted such that the photodiode221 is desirably formed between the surface of the semiconductorsubstrate 211 and a depth of 5 μm to 15 μm for visible light, and is forexample formed between the surface of the semiconductor substrate 211and a depth of about 5 μm.

As described above, an N-type substrate is used as the silicon substrate211, and therefore isolation of the photodiode 221 is performed by theP-type well region 212.

Next, MOS type transistors within a pixel are formed.

As shown in FIG. 15B, a gate insulating film 231 is formed on thesilicon substrate 211, and then a polysilicon film for forming gateelectrodes is formed. Next, a resist mask (not shown) to serve as anetching mask for forming the gate electrodes is formed on thepolysilicon film. With the resist mask used as etching mask, thepolysilicon film is patterned, whereby the gate electrodes 232 of atransfer transistor, a reset transistor, an amplifying transistor, and aselecting transistor are formed by polysilicon.

Next, as shown in FIG. 15C, side walls 233 are formed on the side partof each of the gate electrodes 232 for a purpose of suppressing a shortchannel effect of a MOS transistor (not shown) of a peripheral circuit,the reset transistor, the amplifying transistor, the selectingtransistor, and the like. The side walls 233 are formed by a siliconoxide film, for example. However, the side walls 233 can be formed by asilicon nitride film.

Next, a resist mask (not shown) is formed, and diffusion layers 234,235, 236, and 237 serving as sources and drains of the transistors areformed in the semiconductor substrate 211 by ion implantation using theresist mask.

In general, when holes and electrons are compared with each other ascarriers, holes are more easily trapped on the gate insulating film 231and the interface. Thus, this time, electrons are selected as carriers,that is, N-MOS is formed. A floating diffusion 226 is also formed at thesame time by the ion implantation.

Next, as shown in FIG. 15D, silicide layers 241 to 249 are formed on thediffusion layers 234 to 237, on the floating diffusion 226, and on thegate electrodes 232, respectively, by a salicide process.

Prior to the salicide process, because silicide layers have low opticaltransparency, a silicide blocking film 251 is formed on the photodiode221 to prevent the formation of a silicide layer on the photodiode 221.The silicide blocking film 251 is desirably formed by a silicon oxidefilm, a silicon nitride film, a silicon oxynitride film or the like. Atitanium silicide, a tantalum silicide, a molybdenum silicide, a nickelsilicide, a tungsten silicide, a nickel-platinum silicide or the likecan be applied as the silicide layers 241 to 249.

Next, as shown in FIG. 15E, an etching stopper film 252 for temporarilystopping etching at a time of contact processing is formed on an entiresurface over the silicon substrate 211. The etching stopper film 252 isformed by a silicon nitride film, a silicon oxynitride film or the likethat makes it easy to secure a selective etching ratio with respect to asilicon oxide film as an interlayer insulating film to be formed later.

Thereafter, though not shown, an interlayer insulating film is formed,and a contact part is formed using tungsten.

Further, a wiring layer, an interlayer insulating film, a planarizinginsulating film, a color filter layer, and a microchip lens, and thelike are formed, whereby the CMOS image sensor is completed.

However, in the above-described CMOS image sensor, variations in 1/fnoise increase significantly due not only to a finer design rule of theamplifying transistor (AMP) but also to the load of tensile stress onthe channel part by the silicide layers 243 and 244 of the amplifyingtransistor 224. As a result, the SN ratio is lowered, and it isdifficult to obtain sufficient image quality.

SUMMARY OF THE INVENTION

A problem to be solved is that when a silicide layer is introduced intoa transistor within a pixel or the like to miniaturize the pixel,variations in 1/f noise increase significantly due to the load oftensile stress on the channel part of the transistor by the silicidelayer, so that the SN ratio is lowered and thus sufficient image qualitycannot be obtained.

The present invention makes it possible to prevent the lowering of theSN ratio by suppressing increase in variation in 1/f noise and thusobtain sufficient image quality even when a silicide layer is introducedinto a transistor to miniaturize the pixel.

According to an embodiment of the present invention, there is provided asolid-state image pickup device including: a photoelectric conversionsection configured to convert incident light into a signal charge; atransfer transistor configured to read the signal charge from thephotoelectric conversion section and transfer the signal charge; and anamplifying transistor configured to amplify the signal charge read bythe transfer transistor, wherein a compressive stress film for applyinga compressive stress to a channel part of the amplifying transistor isformed on the amplifying transistor.

In the solid-state image pickup device according to the above-describedembodiment of the present invention, the compressive stress film isformed on the amplifying transistor. Therefore, a local tensile stressapplied to a channel region of the amplifying transistor is relieved bythe compressive stress of the compressive stress film, so that anincrease in variation in 1/f noise of the amplifying transistor can besuppressed.

According to an embodiment of the present invention, there is provided amethod of manufacturing a solid-state image pickup device, thesolid-state image pickup device including, in a semiconductor substrate,a photoelectric conversion section configured to convert incident lightinto a signal charge, a transfer transistor configured to read thesignal charge from the photoelectric conversion section and transfer thesignal charge, and an amplifying transistor configured to amplify thesignal charge read by the transfer transistor. The method includes thesteps of: forming, after forming the amplifying transistor in thesemiconductor substrate, an insulating film on the semiconductorsubstrate, the insulating film having an opening part on the amplifyingtransistor; forming a compressive stress film covering the amplifyingtransistor and having a compressive stress on the insulating film; andleaving the compressive stress film only on the amplifying transistorand removing the compressive stress film on other regions.

In the method of manufacturing the solid-state image pickup deviceaccording to the above-described embodiment of the present invention,the compressive stress film is formed on the amplifying transistor.Therefore, a local tensile stress applied to a channel region of theamplifying transistor is relieved by the compressive stress of thecompressive stress film, so that an increase in variation in 1/f noiseof the amplifying transistor can be suppressed.

According to an embodiment of the present invention, there is provided amethod of manufacturing a solid-state image pickup device, thesolid-state image pickup device including, in a semiconductor substrate,a photoelectric conversion section configured to convert incident lightinto a signal charge, a transfer transistor configured to read thesignal charge from the photoelectric conversion section and transfer thesignal charge, and an amplifying transistor configured to amplify thesignal charge read by the transfer transistor. The method includes thesteps of: forming, after forming the amplifying transistor in thesemiconductor substrate, a compressive stress film covering theamplifying transistor and having a compressive stress on thesemiconductor substrate; and leaving the compressive stress film only onthe amplifying transistor and removing the compressive stress film onregions other than on the amplifying transistor.

In the method of manufacturing the solid-state image pickup deviceaccording to the above-described embodiment of the present invention,the compressive stress film is formed on the amplifying transistor.Therefore, a local tensile stress applied to a channel region of theamplifying transistor is relieved by the compressive stress of thecompressive stress film, so that an increase in variation in 1/f noiseof the amplifying transistor can be suppressed.

A solid-state image pickup device according to an embodiment of thepresent invention can suppress an increase in variation in 1/f noise ofthe amplifying transistor. Thus, because the lowering of the SN ratiocan be suppressed, there is an advantage of being able to obtainexcellent image quality by achieving a high SN ratio.

A method of manufacturing a solid-state image pickup device according toan embodiment of the present invention can suppress an increase invariation in 1/f noise of the amplifying transistor. Thus, because thelowering of the SN ratio can be suppressed, there is an advantage ofbeing able to obtain excellent image quality by achieving a high SNratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration sectional view of an embodiment(first embodiment) of a solid-state image pickup device according to thepresent invention;

FIG. 2 is a circuit configuration diagram of an embodiment (firstembodiment) of a solid-state image pickup device according to thepresent invention;

FIG. 3 is a circuit configuration diagram showing another circuitconfiguration in the first embodiment of the solid-state image pickupdevice;

FIG. 4 is a schematic configuration sectional view of an embodiment(second embodiment) of a solid-state image pickup device according tothe present invention;

FIG. 5 is a schematic configuration sectional view of an embodiment(third embodiment) of a solid-state image pickup device according to thepresent invention;

FIG. 6 is a schematic configuration sectional view of an embodiment(fourth embodiment) of a solid-state image pickup device according tothe present invention;

FIGS. 7A to 7I are manufacturing process sectional views of anembodiment (first embodiment) of a method of manufacturing a solid-stateimage pickup device according to the present invention;

FIGS. 8A and 8B are manufacturing process sectional views of anembodiment (second embodiment) of a method of manufacturing asolid-state image pickup device according to the present invention;

FIG. 9 is a manufacturing process sectional view of an embodiment (thirdembodiment) of a method of manufacturing a solid-state image pickupdevice according to the present invention;

FIG. 10 is a manufacturing process sectional view of an embodiment(fourth embodiment) of a method of manufacturing a solid-state imagepickup device according to the present invention;

FIG. 11 is a manufacturing process sectional view of an embodiment(fifth embodiment) of a method of manufacturing a solid-state imagepickup device according to the present invention;

FIGS. 12A to 12E are manufacturing process sectional views of anembodiment (sixth embodiment) of a method of manufacturing a solid-stateimage pickup device according to the present invention;

FIG. 13 is a schematic perspective sectional view of a CMOS image sensorof a back-surface irradiation type;

FIG. 14 is a schematic configuration sectional view of an example of asolid-state image pickup device in related art; and

FIG. 15A to 15E are manufacturing process sectional views of an exampleof a method of manufacturing the solid-state image pickup device inrelated art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment (first embodiment) of a solid-state image pickup deviceaccording to the present invention will be described with reference to aschematic configuration sectional view of FIG. 1 and a circuitconfiguration diagram of FIG. 2. The solid-state image pickup device isa CMOS image sensor. FIG. 1 shows a sensor section of a pixel section ofthe CMOS image sensor and a group of transistors within the pixel. FIG.2 shows an example of a circuit configuration of the CMOS image sensor.

Description will be made below with reference to FIG. 1 and FIG. 2.

A semiconductor substrate 11 of a first conduction type has a wellregion 12 of a second conduction type formed therein, the secondconduction type being an opposite conduction type from the firstconduction type. Description in the following will be made supposingthat, as an example, the first conduction type is an N-type and thesecond conduction type is a P-type. For example an N-type siliconsubstrate is used as the above-described semiconductor substrate 11.

A photoelectric conversion section (for example a photodiode (PD)) 21for converting incident light into a signal charge is formed at apredetermined position on the surface side of the semiconductorsubstrate 11. The photoelectric conversion section 21 will hereinafterbe described as photodiode 21.

The photodiode 21 is for example formed by a P-type region, an N-typeregion, and a P-type region from a bottom layer in the semiconductorsubstrate 11. The photodiode 21 is desirably formed between the surfaceof the semiconductor substrate 11 and a depth of 5 μm to 15 μm forvisible light, and is for example formed between the surface of thesemiconductor substrate 11 and a depth of about 5 μm.

As described above, an N-type silicon substrate is used as thesemiconductor substrate 11, and therefore element isolation for thephotodiode 21 is performed by the well region 12.

MOS type transistors within the pixel are formed on the semiconductorsubstrate 11.

Gate electrodes 32 are formed on the semiconductor substrate 11 with agate insulating film 31 interposed between the gate electrodes 32 andthe semiconductor substrate 11. These gate electrodes 32 are the gateelectrode 32 (32R) of a reset transistor of the pixel transistor group,the gate electrode 32 (32A) of an amplifying transistor of the pixeltransistor group, and the gate electrode 32 (32S) of a selectingtransistor of the pixel transistor group. Each of the gate electrodes 32is formed by polysilicon, for example.

In addition, the gate electrode 32 (32T) of a transfer transistor forreading the signal charge from the photodiode 21 and transferring thesignal charge is formed adjoining the photodiode 21.

Incidentally, each gate electrode 32 has very fine dimensions of 0.1μm×0.1 μm, for example.

Side walls 33 are formed on the side part of each of the gate electrodes32. The side walls 33 are formed by a silicon oxide film, for example.Alternatively, the side walls 33 may be formed by a silicon nitridefilm.

Diffusion layers 34, 35, 36, and 37 serving as sources and drains of thetransistors are formed in the semiconductor substrate 11 on both sidesof the respective gate electrodes 32. In this case, as an example, thediffusion layer 35 is shared as one diffusion layer 35 of the resettransistor 23 and one diffusion layer 35 of the amplifying transistor24, and the diffusion layer 36 is shared as another diffusion layer 36of the amplifying transistor 24 and one diffusion layer 36 of theselecting transistor 25. A floating diffusion (FD) 26 is also formed inthe semiconductor substrate 11.

In general, when holes and electrons are compared with each other ascarriers, holes are more easily trapped on the gate insulating film 31and the interface. Thus, in this case, electrons are selected ascarriers, that is, NMOS transistors are formed.

Silicide layers 41 to 44, 45, and 46 to 49 are formed on the diffusionlayers 34 to 37, on the floating diffusion 26, and on the gateelectrodes 32, respectively.

In addition, a silicide blocking film 51 is formed on the photodiode 21to prevent the formation of a silicide layer as described above on thephotodiode 21. The silicide blocking film 51 is desirably formed by asilicon oxide film, a silicon nitride film, a silicon oxynitride film orthe like. A titanium silicide, a tantalum silicide, a molybdenumsilicide, a nickel silicide, a tungsten silicide, a nickel-platinumsilicide or the like can be applied as the silicide layers 41 to 49.

The transfer transistor 22 is connected between the cathode electrode ofthe photodiode 21 and the floating diffusion 26 as a charge-voltageconverting section. The transfer transistor 22 transfers the signalcharge (electrons in this case) stored in the photodiode 21 as a resultof photoelectric conversion by the photodiode 21 to the floatingdiffusion 26 when a transfer pulse TRG is supplied to the gate electrode(control electrode) 32TG.

The reset transistor 23 has a drain electrode (diffusion layer 35)connected to a reset line, and has a source electrode (diffusion layer34) connected to the floating diffusion 26. When a reset pulse RST issupplied to the gate electrode 32R prior to the transfer of the signalcharge from the photodiode 21 to the floating diffusion 26, the resettransistor 23 resets the potential of the floating diffusion 26 to areset voltage Vrst.

The amplifying transistor 24 has the gate electrode 32A connected to thefloating diffusion 26, and has a drain electrode (common diffusion layer35) connected to a pixel power supply Vdd. The amplifying transistor 24outputs the potential of the floating diffusion 26 after being reset bythe reset transistor 23 as a reset level, and outputs the potential ofthe floating diffusion 26 after the transfer transistor 22 transfers thesignal charge as a signal level.

The selecting transistor 25 for example has a drain electrode (diffusionlayer 36) connected to the source electrode (common diffusion layer 36)of the amplifying transistor 24, and has a source electrode connected toan output signal line. When a selecting pulse SEL is supplied to thegate electrode 32S, the selecting transistor 25 is set in an on state,and outputs a signal output from the amplifying transistor 24 with thepixel in a selected state to the output signal line (wiring 75).Incidentally, the selecting transistor 25 can also be connected betweenthe pixel power supply Vdd and the drain electrode of the amplifyingtransistor 24.

An etching stopper film 52 having an opening 53 formed on the amplifyingtransistor 24 is formed on an entire surface over the semiconductorsubstrate 11. The etching stopper film 52 is formed by a silicon nitridefilm, a silicon oxynitride film or the like that makes it easy to securea selective etching ratio with respect to a silicon oxide film as aninterlayer insulating film to be formed later.

On the other hand, a compressive stress film 54 having a compressivestress is formed on the amplifying transistor 24 so as to cover theamplifying transistor 24. This compressive stress film 54 is formed by asilicon oxide film, for example.

The etching stopper film 52 and the compressive stress film 54 aredesirably of different film species because different film species makeit easy to secure a processing (etching) selectivity. For example, asdescribed above, the etching stopper film 52 is formed by a siliconnitride film, and the compressive stress film 54 is formed by a siliconoxide film. Of course, it may be vice versa, or two species of a siliconnitride film, a silicon oxide film, and a silicon oxynitride film can beselected and used.

When the etching stopper film 52 and the compressive stress film 54 areof a same species, a structure having an intermediate film of adifferent species inserted between the etching stopper film 52 and thecompressive stress film 54 is desirable.

Though not shown, for example, when a silicon nitride film is applied asthe etching stopper film 52, a silicon oxide film is applied as theintermediate film.

Further formed are for example wiring 71 for connecting the transfertransistor electrode 32T and a driving circuit (not shown) to eachother, wiring 72 for connecting the gate electrode 32R of the resettransistor 23 and the driving circuit (not shown) to each other, wiring73 for connecting the gate electrode 32A of the amplifying transistor 24and the floating diffusion 26 to each other, wiring 74 for connectingthe gate electrode 32S of the selecting transistor 25 and the drivingcircuit (not shown) to each other, wiring 75 for connecting thediffusion layer 37 of the selecting transistor 25 and a horizontalscanning circuit (output) (not shown) to each other, wiring 76 forconnecting the diffusion layer 35 shared between the reset transistor 23and the amplifying transistor 24 and the pixel power supply Vdd (notshown) to each other, and the like.

In the solid-state image pickup device 1 according to the presentembodiment, the compressive stress film 54 having a compressive stressis formed on the amplifying transistor 24. Therefore, a local tensilestress applied to a channel region of the amplifying transistor 24 whichstress is caused by the silicide layers 42 and 43 formed on thediffusion layers 35 and 36 of the amplifying transistor 24 is relievedby the compressive stress of the compressive stress film 54, so that anincrease in variation in 1/f noise of the amplifying transistor 24 canbe suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

The circuit configuration of a pixel transistor section shown by FIG. 2may be formed as shown in FIG. 3.

As shown in FIG. 3, a photodiode 21 is provided, and a transfertransistor 22 is provided so as to be connected to the photodiode 21.The transfer transistor 22 is connected between the cathode electrode ofthe photodiode 21 and a floating diffusion 26 as a charge-voltageconverting section. The transfer transistor 22 transfers a signal charge(electrons in this case) stored in the photodiode 21 as a result ofphotoelectric conversion by the photodiode 21 to the floating diffusion26 when a transfer pulse TRG is supplied to the gate electrode (controlelectrode) 32TG.

A reset transistor 23 has a drain electrode (diffusion layer 35)connected to a pixel power supply Vdd, and has a source electrode(diffusion layer 34) connected to the floating diffusion 26. When areset pulse RST is supplied to the gate electrode 32R prior to thetransfer of the signal charge from the photodiode 21 to the floatingdiffusion 26, the reset transistor 23 resets the potential of thefloating diffusion 26 to a reset voltage Vrst.

An amplifying transistor 24 has a gate electrode 32A connected to thefloating diffusion 26. The amplifying transistor 24 outputs thepotential of the floating diffusion 26 after being reset by the resettransistor 23 as a reset level, and outputs the potential of thefloating diffusion 26 after the transfer transistor 22 transfers thesignal charge as a signal level.

A selecting transistor 25 for example has a drain electrode (diffusionlayer 36) connected to the source electrode (common diffusion layer 36)of the amplifying transistor 24, and has a source electrode connected toan output signal line. When a selecting pulse SEL is supplied to thegate electrode 32S, the selecting transistor 25 is set in an on state,and outputs a signal output from the amplifying transistor 24 with thepixel in a selected state to the output signal line (wiring 75).

An example in which a compressive stress film is formed without anetching stopper film being formed will next be described as anembodiment (second embodiment) of a solid-state image pickup deviceaccording to the present invention with reference to a schematicconfiguration sectional view of FIG. 4.

In the foregoing first embodiment, the etching stopper film is formed toprevent excessive etching into the diffusion layers when a contact isformed. When the etching stopper film is not required, a compressivestress film is formed without the etching stopper film being formed.

A solid-state image pickup device in this case (second embodiment) willbe described in the following.

As shown in FIG. 4, a semiconductor substrate 11 of a first conductiontype has a well region 12 of a second conduction type formed therein,the second conduction type being an opposite conduction type from thefirst conduction type. Description in the following will be madesupposing that, as an example, the first conduction type is an N-typeand the second conduction type is a P-type. For example an N-typesilicon substrate is used as the above-described semiconductor substrate11.

A photoelectric conversion section (for example a photodiode (PD)) 21for converting incident light into a signal charge is formed at apredetermined position on the surface side of the semiconductorsubstrate 11.

The photodiode 21 is for example formed by a P-type region, an N-typeregion, and a P-type region from a bottom layer in the semiconductorsubstrate 11. The photodiode 21 is desirably formed between the surfaceof the semiconductor substrate 11 and a depth of 5 μm to 15 μm forvisible light, and is for example formed between the surface of thesemiconductor substrate 11 and a depth of about 5 μm.

As described above, an N-type silicon substrate is used as thesemiconductor substrate 11, and therefore element isolation for thephotodiode 21 is performed by the well region 12.

MOS type transistors within the pixel are formed on the semiconductorsubstrate 11.

Gate electrodes 32 are formed on the semiconductor substrate 11 with agate insulating film 31 interposed between the gate electrodes 32 andthe semiconductor substrate 11. These gate electrodes 32 are the gateelectrode 32 (32R) of a reset transistor of the pixel transistor group,the gate electrode 32 (32A) of an amplifying transistor of the pixeltransistor group, and the gate electrode 32 (32S) of a selectingtransistor of the pixel transistor group. Each of the gate electrodes 32is formed by polysilicon, for example.

In addition, the gate electrode 32 (32T) of a transfer transistor forreading the signal charge from the photodiode 21 and transferring thesignal charge is formed adjoining the photodiode 21.

Incidentally, each gate electrode 32 has very fine dimensions of 0.1μm×0.1 μm, for example.

Side walls 33 are formed on the side part of each of the gate electrodes32. The side walls 33 are formed by a silicon oxide film, for example.Alternatively, the side walls 33 may be formed by a silicon nitridefilm.

Diffusion layers 34, 35, 36, and 37 serving as sources and drains of thetransistors are formed in the semiconductor substrate 11 on both sidesof the respective gate electrodes 32. In this case, as an example, thediffusion layer 35 is shared as one diffusion layer 35 of the resettransistor 23 and one diffusion layer 35 of the amplifying transistor24, and the diffusion layer 36 is shared as another diffusion layer 36of the amplifying transistor 24 and one diffusion layer 36 of theselecting transistor 25. A floating diffusion (FD) 26 is also formed inthe semiconductor substrate 11.

In general, when holes and electrons are compared with each other ascarriers, holes are more easily trapped on the gate insulating film 31and the interface. Thus, in this case, electrons are selected ascarriers, that is, NMOS transistors are formed.

Silicide layers 41 to 44, 45, and 46 to 49 are formed on the diffusionlayers 34 to 37, on the floating diffusion 26, and on the gateelectrodes 32, respectively.

In addition, a silicide blocking film 51 is formed on the photodiode 21to prevent the formation of a silicide layer as described above on thephotodiode 21. The silicide blocking film 51 is desirably formed by asilicon oxide film, a silicon nitride film, a silicon oxynitride film orthe like. A titanium silicide, a tantalum silicide, a molybdenumsilicide, a nickel silicide, a tungsten silicide, a nickel-platinumsilicide or the like can be applied as the silicide layers 41 to 49.

The transfer transistor 22 is connected between the cathode electrode ofthe photodiode 21 and the floating diffusion 26 as a charge-voltageconverting section. The transfer transistor 22 transfers the signalcharge (electrons in this case) stored in the photodiode 21 as a resultof photoelectric conversion by the photodiode 21 to the floatingdiffusion 26 when a transfer pulse TRG is supplied to the gate electrode(control electrode) 32T.

The reset transistor 23 has a drain electrode (diffusion layer 35)connected to a reset line, and has a source electrode (diffusion layer34) connected to the floating diffusion 26. When a reset pulse RST issupplied to the gate electrode 32R prior to the transfer of the signalcharge from the photodiode 21 to the floating diffusion 26, the resettransistor 23 resets the potential of the floating diffusion 26 to areset voltage Vrst.

The amplifying transistor 24 has the gate electrode 32A connected to thefloating diffusion 26, and has a drain electrode (common diffusion layer35) connected to a pixel power supply Vdd. The amplifying transistor 24outputs the potential of the floating diffusion 26 after being reset bythe reset transistor 23 as a reset level, and outputs the potential ofthe floating diffusion 26 after the transfer transistor 22 transfers thesignal charge as a signal level.

The selecting transistor 25 for example has a drain electrode (diffusionlayer 36) connected to the source electrode (common diffusion layer 36)of the amplifying transistor 24, and has a source electrode connected toan output signal line. When a selecting pulse SEL is supplied to thegate electrode 32S, the selecting transistor 25 is set in an on state,and outputs a signal output from the amplifying transistor 24 with thepixel in a selected state to the output signal line (wiring 75).Incidentally, the selecting transistor 25 can also be connected betweenthe pixel power supply Vdd and the drain electrode of the amplifyingtransistor 24.

A compressive stress film 54 having a compressive stress is formed onthe amplifying transistor 24 so as to cover the amplifying transistor24. This compressive stress film 54 is formed by a silicon nitride filmor a silicon oxide film, for example.

Further formed are for example wiring 71 for connecting the gateelectrode 32T of the transfer transistor 22 and a driving circuit (notshown) to each other, wiring 72 for connecting the gate electrode 32R ofthe reset transistor 23 and the driving circuit (not shown) to eachother, wiring 73 for connecting the gate electrode 32A of the amplifyingtransistor 24 and the floating diffusion 26 to each other, wiring 74 forconnecting the gate electrode 32S of the selecting transistor 25 and thedriving circuit (not shown) to each other, wiring 75 for connecting thediffusion layer 37 of the selecting transistor 25 and a horizontalscanning circuit (output) (not shown) to each other, wiring 76 forconnecting the diffusion layer 35 shared between the reset transistor 23and the amplifying transistor 24 and the pixel power supply Vdd (notshown) to each other, and the like.

In the solid-state image pickup device 2 according to the presentembodiment, the compressive stress film 54 having a compressive stressis formed on the amplifying transistor 24. Therefore, a local tensilestress applied to a channel region of the amplifying transistor 24 whichstress is caused by the silicide layers 42 and 43 formed on thediffusion layers 35 and 36 of the amplifying transistor 24 is relievedby the compressive stress of the compressive stress film 54, so that anincrease in variation in 1/f noise of the amplifying transistor 24 canbe suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

In addition, because the etching stopper film as in the first embodimentis not formed, there is an advantage of being able to reduce each of thenumbers of film formation steps, lithography steps, and etching steps,for example, by one as compared with the solid-state image pickup device1 according to the first embodiment.

An example having an element isolation region of a shallow trenchelement isolation structure made by forming an insulator within agroove, the element isolation region being adjacent to a diffusion layerof an amplifying transistor, will next be described as an embodiment(third embodiment) of a solid-state image pickup device 3 according tothe present invention with reference to a schematic configurationsectional view of FIG.

5.

As shown in FIG. 5, a semiconductor substrate 11 of a first conductiontype has a well region 12 of a second conduction type formed therein,the second conduction type being an opposite conduction type from thefirst conduction type. Description in the following will be madesupposing that, as an example, the first conduction type is an N-typeand the second conduction type is a P-type. For example an N-typesilicon substrate is used as the above-described semiconductor substrate11.

An element isolation region 96 of an STI (Shallow Trench Isolation)structure is formed which separates regions for forming pixeltransistors such as a region for forming a reset transistor, a regionfor forming an amplifying transistor, a region for forming a selectingtransistor, and the like formed in the semiconductor substrate 11.

A photoelectric conversion section (for example a photodiode (PD)) 21for converting incident light into a signal charge is formed at apredetermined position on the surface side of the semiconductorsubstrate 11.

The photodiode 21 is for example formed by a P-type region, an N-typeregion, and a P-type region from a bottom layer in the semiconductorsubstrate 11. The photodiode 21 is desirably formed between the surfaceof the semiconductor substrate 11 and a depth of 5 μm to 15 μm forvisible light, and is for example formed between the surface of thesemiconductor substrate 11 and a depth of about 5 μm.

As described above, an N-type silicon substrate is used as thesemiconductor substrate 11, and therefore element isolation for thephotodiode 21 is performed by the well region 12.

MOS type transistors within the pixel are formed on the semiconductorsubstrate 11.

Gate electrodes 32 are formed on the semiconductor substrate 11 with agate insulating film 31 interposed between the gate electrodes 32 andthe semiconductor substrate 11. These gate electrodes 32 are the gateelectrode 32 (32R) of the reset transistor of the pixel transistorgroup, the gate electrode 32 (32S) of the selecting transistor of thepixel transistor group, and the gate electrode 32 (32A) of theamplifying transistor of the pixel transistor group. Each of the gateelectrodes 32 is formed by polysilicon, for example.

In addition, the gate electrode 32 (32T) of a transfer transistor forreading the signal charge from the photodiode 21 and transferring thesignal charge is formed adjoining the photodiode 21.

Incidentally, each gate electrode 32 has very fine dimensions of 0.1μm×0.1 μm, for example.

Side walls 33 are formed on the side part of each of the gate electrodes32. The side walls 33 are formed by a silicon oxide film, for example.Alternatively, the side walls 33 may be formed by a silicon nitridefilm.

Diffusion layers 34, 35, 38, and 39 serving as sources and drains of thetransistors are formed in the semiconductor substrate 11 on both sidesof the respective gate electrodes 32. In this case, as an example, thediffusion layer 35 is shared as one diffusion layer 35 of the resettransistor 23 and one diffusion layer 35 of the amplifying transistor24, and the diffusion layer 36 is shared as another diffusion layer 36of the amplifying transistor 24 and one diffusion layer 36 of theselecting transistor 25. A floating diffusion (FD) 26 is also formed inthe semiconductor substrate 11.

In general, when holes and electrons are compared with each other ascarriers, holes are more easily trapped on the gate insulating film 31and the interface. Thus, in this case, electrons are selected ascarriers, that is, NMOS transistors are formed.

Silicide layers 41, 42, 101, and 102, 45, and 46 to 49 are formed so asto correspond to the diffusion layers 34, 35, 38, and 39, the floatingdiffusion 26, and the gate electrodes 32, respectively.

In addition, a silicide blocking film 51 is formed on the photodiode 21to prevent the formation of a silicide layer as described above on thephotodiode 21. The silicide blocking film 51 is desirably formed by asilicon oxide film, a silicon nitride film, a silicon oxynitride film orthe like. A titanium silicide, a tantalum silicide, a molybdenumsilicide, a nickel silicide, a tungsten silicide, a nickel-platinumsilicide or the like can be applied as the silicide layers 41, 42, 101,and 102 and 45 to 49.

The transfer transistor 22 is connected between the cathode electrode ofthe photodiode 21 and the floating diffusion 26 as a charge-voltageconverting section. The transfer transistor 22 transfers the signalcharge (electrons in this case) stored in the photodiode 21 as a resultof photoelectric conversion by the photodiode 21 to the floatingdiffusion 26 when a transfer pulse TRG is supplied to the gate electrode(control electrode) 32T.

The reset transistor 23 has a drain electrode (diffusion layer 35)connected to a reset line, and has a source electrode (diffusion layer34) connected to the floating diffusion 26. When a reset pulse RST issupplied to the gate electrode 32R prior to the transfer of the signalcharge from the photodiode 21 to the floating diffusion 26, the resettransistor 23 resets the potential of the floating diffusion 26 to areset voltage Vrst.

The amplifying transistor 24 has the gate electrode 32A connected to thefloating diffusion 26. The amplifying transistor 24 outputs thepotential of the floating diffusion 26 after being reset by the resettransistor 23 as a reset level, and outputs the potential of thefloating diffusion 26 after the transfer transistor 22 transfers thesignal charge as a signal level.

The selecting transistor 25 for example has a drain electrode (diffusionlayer 38) connected to the source electrode (common diffusion layer 38)of the amplifying transistor 24, and has a source electrode connected toan output signal line. When a selecting pulse SEL is supplied to thegate electrode 32S, the selecting transistor 25 is set in an on state,and outputs a signal output from the amplifying transistor 24 with thepixel in a selected state to the output signal line (wiring 75).

An etching stopper film 52 having an opening 53 formed on the amplifyingtransistor 24 is formed on an entire surface over the semiconductorsubstrate 11. The etching stopper film 52 is formed by a silicon nitridefilm, a silicon oxynitride film or the like that makes it easy to securea selective etching ratio with respect to a silicon oxide film as aninterlayer insulating film to be formed later.

On the other hand, a compressive stress film 54 having a compressivestress is formed on the amplifying transistor 24 so as to cover theamplifying transistor 24. This compressive stress film 54 is formed by asilicon oxide film, for example.

The etching stopper film 52 and the compressive stress film 54 aredesirably of different film species because different film species makeit easy to secure a processing (etching) selectivity. For example, asdescribed above, the etching stopper film 52 is formed by a siliconnitride film, and the compressive stress film 54 is formed by a siliconoxide film. Of course, it may be vice versa, or two species of a siliconnitride film, a silicon oxide film, and a silicon oxynitride film can beselected and used.

When the etching stopper film 52 and the compressive stress film 54 areof a same species, a structure having an intermediate film of adifferent species inserted between the etching stopper film 52 and thecompressive stress film 54 is desirable.

Though not shown, for example, when a silicon nitride film is applied asthe etching stopper film 52, a silicon oxide film is applied as theintermediate film.

Further formed are for example wiring 71 for connecting the gateelectrode 32T of the transfer transistor 22 and a driving circuit (notshown) to each other, wiring 72 for connecting the gate electrode 32R ofthe reset transistor 23 and the driving circuit (not shown) to eachother, wiring 73 for connecting the gate electrode 32A of the amplifyingtransistor 24 and the floating diffusion 26 to each other, wiring 74 forconnecting the gate electrode 32S of the selecting transistor 25 and thedriving circuit (not shown) to each other, wiring 75 for connecting thediffusion layer 39 of the amplifying transistor 24 and a horizontalscanning circuit (output) (not shown) to each other, wiring 76 forconnecting the diffusion layer 35 shared between the reset transistor 23and the selecting transistor 25 and the pixel power supply Vdd (notshown) to each other, and the like.

In the solid-state image pickup device 3 according to the presentembodiment, the compressive stress film 54 having a compressive stressis formed on the amplifying transistor 24. Therefore, a local tensilestress applied to a channel region of the amplifying transistor 24 whichstress is caused by the silicide layers 101 and 102 formed on thediffusion layers 38 and 39 of the amplifying transistor 24 and theelement isolation region 96 is relieved by the compressive stress of thecompressive stress film 54, so that an increase in variation in 1/fnoise of the amplifying transistor 24 can be suppressed.

Hence, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

Thus, noise is reduced, whereby an STI element isolation region can beformed for isolation between elements. It is therefore possible to forma narrower space between elements, and achieve a higher degree ofintegration.

An embodiment (fourth embodiment) of a solid-state image pickup device 4according to the present invention will next be described with referenceto a schematic configuration sectional view of FIG. 6.

As shown in FIG. 6, a semiconductor substrate 11 of a first conductiontype has a well region 12 of a second conduction type formed therein,the second conduction type being an opposite conduction type from thefirst conduction type. Description in the following will be madesupposing that, as an example, the first conduction type is an N-typeand the second conduction type is a P-type. For example an N-typesilicon substrate is used as the above-described semiconductor substrate11.

A photoelectric conversion section (for example a photodiode (PD)) 21for converting incident light into a signal charge is formed at apredetermined position on the surface side of the semiconductorsubstrate 11. The photoelectric conversion section 21 will hereinafterbe described as photodiode 21.

The photodiode 21 is for example formed by a P-type region, an N-typeregion, and a P-type region from a bottom layer in the semiconductorsubstrate 11. The photodiode 21 is desirably formed between the surfaceof the semiconductor substrate 11 and a depth of 5 μm to 15 μm forvisible light, and is for example formed between the surface of thesemiconductor substrate 11 and a depth of about 5 μm.

As described above, an N-type silicon substrate is used as thesemiconductor substrate 11, and therefore element isolation for thephotodiode 21 is performed by the well region 12.

MOS type transistors within the pixel are formed on the semiconductorsubstrate 11.

Gate electrodes 32 are formed on the semiconductor substrate 11 with agate insulating film 31 interposed between the gate electrodes 32 andthe semiconductor substrate 11. These gate electrodes 32 are the gateelectrode 32 (32R) of a reset transistor of the pixel transistor group,the gate electrode 32 (32A) of an amplifying transistor of the pixeltransistor group, and the gate electrode 32 (32S) of a selectingtransistor of the pixel transistor group. Each of the gate electrodes 32is formed by polysilicon, for example.

In addition, the gate electrode 32 (32T) of a transfer transistor forreading the signal charge from the photodiode 21 and transferring thesignal charge is formed adjoining the photodiode 21.

Side walls 33 are formed on the side part of each of the gate electrodes32. The side walls 33 are formed by a silicon nitride film, for example.

In particular, the side walls 33 (33A) formed on the side walls of thegate electrode 32A of the amplifying transistor 24 are formed by acompressive stress film having a compressive stress. Such a compressivestress film is for example formed by subjecting only the silicon nitridefilm formed on the side walls of the gate electrode 32 of the amplifyingtransistor 24 to electron beam irradiation or to nitrogen ionimplantation and heat treatment (for example RTA (Rapid ThermalAnnealing)). Of course, the compressive stress film may be formed byother manufacturing methods.

Diffusion layers 34, 35, 36, and 37 serving as sources and drains of thetransistors are formed in the semiconductor substrate 11 on both sidesof the respective gate electrodes 32. In this case, as an example, thediffusion layer 35 is shared as one diffusion layer 35 of the resettransistor 23 and one diffusion layer 35 of the amplifying transistor24, and the diffusion layer 36 is shared as another diffusion layer 36of the amplifying transistor 24 and one diffusion layer 36 of theselecting transistor 25. A floating diffusion (FD) 26 is also formed inthe semiconductor substrate 11.

In general, when holes and electrons are compared with each other ascarriers, holes are more easily trapped on the gate insulating film 31and the interface. Thus, in this case, electrons are selected ascarriers, that is, NMOS transistors are formed.

Silicide layers 41 to 44, 45, and 46 to 49 are formed on the diffusionlayers 34 to 37, on the floating diffusion 26, and on the gateelectrodes 32, respectively.

In addition, a silicide blocking film 51 is formed on the photodiode 21to prevent the formation of a silicide layer as described above on thephotodiode 21. The silicide blocking film 51 is desirably formed by asilicon oxide film, a silicon nitride film, a silicon oxynitride film orthe like. A titanium silicide, a tantalum silicide, a molybdenumsilicide, a nickel silicide, a tungsten silicide, a nickel-platinumsilicide or the like can be applied as the silicide layers 41 to 49.

The transfer transistor 22 is connected between the cathode electrode ofthe photodiode 21 and the floating diffusion 26 as a charge-voltageconverting section. The transfer transistor 22 transfers the signalcharge (electrons in this case) stored in the photodiode 21 as a resultof photoelectric conversion by the photodiode 21 to the floatingdiffusion 26 when a transfer pulse TRG is supplied to the gate electrode(control electrode) 32T.

The reset transistor 23 has a drain electrode (diffusion layer 35)connected to a reset line, and has a source electrode (diffusion layer34) connected to the floating diffusion 26. When a reset pulse RST issupplied to the gate electrode 32R prior to the transfer of the signalcharge from the photodiode 21 to the floating diffusion 26, the resettransistor 23 resets the potential of the floating diffusion 26 to areset voltage Vrst.

The amplifying transistor 24 has the gate electrode 32A connected to thefloating diffusion 26, and has a drain electrode (common diffusion layer35) connected to a pixel power supply Vdd. The amplifying transistor 24outputs the potential of the floating diffusion 26 after being reset bythe reset transistor 23 as a reset level, and outputs the potential ofthe floating diffusion 26 after the transfer transistor 22 transfers thesignal charge as a signal level.

The selecting transistor 25 for example has a drain electrode (diffusionlayer 36) connected to the source electrode (common diffusion layer 36)of the amplifying transistor 24, and has a source electrode connected toan output signal line. When a selecting pulse SEL is supplied to thegate electrode 32S, the selecting transistor 25 is set in an on state,and outputs a signal output from the amplifying transistor 24 with thepixel in a selected state to the output signal line (wiring 75).Incidentally, the selecting transistor 25 can also be connected betweenthe pixel power supply Vdd and the drain electrode of the amplifyingtransistor 24.

An etching stopper film 52 having an opening 53 formed on the amplifyingtransistor 24 is formed on an entire surface over the semiconductorsubstrate 11. The etching stopper film 52 is formed by a silicon nitridefilm, a silicon oxynitride film or the like that makes it easy to securea selective etching ratio with respect to a silicon oxide film as aninterlayer insulating film to be formed later.

On the other hand, a compressive stress film 54 having a compressivestress is formed on the amplifying transistor 24 so as to cover theamplifying transistor 24. This compressive stress film 54 is formed by asilicon oxide film, for example.

The etching stopper film 52 and the compressive stress film 54 aredesirably of different film species because different film species makeit easy to secure a processing (etching) selectivity. For example, asdescribed above, the etching stopper film 52 is formed by a siliconnitride film, and the compressive stress film 54 is formed by a siliconoxide film. Of course, it may be vice versa, or two species of a siliconnitride film, a silicon oxide film, and a silicon oxynitride film can beselected and used.

When the etching stopper film 52 and the compressive stress film 54 areof a same species, a structure having an intermediate film of adifferent species inserted between the etching stopper film 52 and thecompressive stress film 54 is desirable.

Though not shown, for example, when a silicon nitride film is applied asthe etching stopper film 52, a silicon oxide film is applied as theintermediate film.

Further formed are for example wiring 71 for connecting the gateelectrode 32T of the transfer transistor and a driving circuit (notshown) to each other, wiring 72 for connecting the gate electrode 32R ofthe reset transistor 23 and the driving circuit (not shown) to eachother, wiring 73 for connecting the gate electrode 32A of the amplifyingtransistor 24 and the floating diffusion 26 to each other, wiring 74 forconnecting the gate electrode 32S of the selecting transistor 25 and thedriving circuit (not shown) to each other, wiring 75 for connecting thediffusion layer 37 of the selecting transistor 25 and a horizontalscanning circuit (output) (not shown) to each other, wiring 76 forconnecting the diffusion layer 35 shared between the reset transistor 23and the amplifying transistor 24 and the pixel power supply Vdd (notshown) to each other, and the like.

In the solid-state image pickup device 4 according to the presentembodiment, the compressive stress film 54 having a compressive stressis formed on the amplifying transistor 24. Therefore, a local tensilestress applied to a channel region of the amplifying transistor 24 whichstress is caused by the silicide layers 42 and 43 formed on thediffusion layers 35 and 36 of the amplifying transistor 24 is relievedby the compressive stress of the compressive stress film 54 and thecompressive stress of the side walls 33A formed by a compressive stressfilm, so that an increase in variation in 1/f noise of the amplifyingtransistor 24 can be suppressed more than in the first to thirdembodiments.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

The fourth embodiment is applicable to the second and third embodiments.

An embodiment (first embodiment) of a method of manufacturing asolid-state image pickup device according to the present invention willnext be described with reference to manufacturing process sectionalviews of FIGS. 7A to 7I.

As shown in FIG. 7A, in a semiconductor substrate 11 of a firstconduction type, a well region 12 of a second conduction type is formed,the second conduction type being an opposite conduction type from thefirst conduction type. Description in the following will be madesupposing that, as an example, the first conduction type is an N-typeand the second conduction type is a P-type. For example an N-typesilicon substrate is used as the above-described semiconductor substrate11.

Next, a photodiode (PD) 21 for performing photoelectric conversion isformed at a predetermined position on the surface side of thesemiconductor substrate 11. The photodiode 21 is for example formed by aP-type region, an N-type region, and a P-type region from a bottom layerby performing ion implantation of phosphorus (P) as an N-type impurityand boron (B) as a P-type impurity using an ion implantation mask formedby patterning a resist film formed on the semiconductor substrate 11.The energy of the ion implantation is adjusted such that the photodiode21 is desirably formed between the surface of the semiconductorsubstrate 11 and a depth of 5 μm to 15 μm for visible light, and is forexample formed between the surface of the semiconductor substrate 11 anda depth of about 5 μm.

As described above, an N-type silicon substrate is used as thesemiconductor substrate 11, and therefore element isolation for thephotodiode 21 is performed by the well region 12.

Thereafter, the ion implantation mask formed by the resist film isremoved.

Next, MOS type transistors within a pixel are formed.

As shown in FIG. 7B, a gate insulating film 31 is formed on thesemiconductor substrate 11, and then an electrode forming film forforming gate electrodes is formed. The electrode forming film is formedby polysilicon, for example.

Next, a resist mask (not shown) to serve as an etching mask for formingthe gate electrodes is formed on the electrode forming film. Theelectrode forming film is patterned using the resist mask as etchingmask, whereby the gate electrodes 32 made of the electrode forming filmare formed. These gate electrodes 32 are the gate electrode 32 (32R) ofa reset transistor of a pixel transistor group, the gate electrode 32(32A) of an amplifying transistor of the pixel transistor group, and thegate electrode 32 (32S) of a selecting transistor of the pixeltransistor group.

In addition, the gate electrode 32 (32T) of a transfer transistor isformed at the same time.

Incidentally, each gate electrode 32 has very fine dimensions of 0.1μm×0.1 μm, for example.

Thereafter the resist mask used as the etching mask is removed.

Next, as shown in FIG. 7C, side walls 33 are formed on the side part ofeach of the gate electrodes 32 for a purpose of suppressing a shortchannel effect of a peripheral circuit, the pixel transistors and thelike. The side walls 33 are formed by a silicon oxide film, for example.Alternatively, the side walls 33 can be formed by a silicon nitridefilm.

Next, a resist mask (not shown) is formed by ordinary resist coating andlithography techniques, and diffusion layers 34, 35, 36, and 37 servingas sources and drains of the transistors are formed by ion implantationusing the resist mask. In this case, as an example, the diffusion layer35 is shared as one diffusion layer 35 of the reset transistor 23 andone diffusion layer 35 of the amplifying transistor 24, and thediffusion layer 36 is shared as another diffusion layer 36 of theamplifying transistor 24 and one diffusion layer 36 of the selectingtransistor 25.

In general, when holes and electrons are compared with each other ascarriers, holes are more easily trapped on the gate insulating film 31and the interface. Thus, in this case, electrons are selected ascarriers, that is, NMOS transistors are formed. A floating diffusion(FD) 26 is also formed in the semiconductor substrate 11 at the sametime by the ion implantation.

Thereafter, the resist mask used as mask for the ion implantation isremoved.

Next, as shown in FIG. 7D, silicide layers 41 to 44, 45, and 46 to 49are formed on the diffusion layers 34 to 37, on the floating diffusion26, and on the gate electrodes 32, respectively, by a salicide process.

Prior to the salicide process, because silicide layers have low opticaltransparency, a silicide blocking film 51 is formed on the photodiode 21to prevent the formation of a silicide layer on the photodiode 21. Thesilicide blocking film 51 is desirably formed by a silicon oxide film, asilicon nitride film, a silicon oxynitride film or the like. A titaniumsilicide, a tantalum silicide, a molybdenum silicide, a nickel silicide,a tungsten silicide, a nickel-platinum silicide or the like can beapplied as the silicide layers 41 to 49.

Next, as shown in FIG. 7E, an etching stopper film 52 for temporarilystopping etching at a time of contact processing is formed on an entiresurface over the semiconductor substrate 11. The etching stopper film 52is formed by a silicon nitride film, a silicon oxynitride film or thelike that makes it easy to secure a selective etching ratio with respectto a silicon oxide film as an interlayer insulating film to be formedlater.

Next, a resist film 61 is formed on the etching stopper film 52 byordinary resist coating techniques. A resist for KrF, for example, isused as the resist film 61. Next, the resist film 61 over the amplifyingtransistor 24 is removed to form an opening 62 by ordinary lithographytechniques.

Next, the etching stopper film 52 on the amplifying transistor 24 isremoved with the resist film 61 used as an etching mask.

As a result, as shown in FIG. 7F, an opening 53 is formed in the etchingstopper film 52 on the amplifying transistor 24. This etching isperformed by reactive ion etching (RIE) using for example a fluorocarbon(CF) base gas as an etching gas.

Thereafter the resist film 61 (see FIG. 7E) is removed.

Next, a compressive stress film 54 having a compressive stress is formedon the etching stopper film 52 so as to cover the top of the amplifyingtransistor 24. This compressive stress film 54 is formed by a siliconoxide film, for example.

Next, as shown in FIG. 7G, a resist film 63 is formed on the compressivestress film 54 by ordinary resist coating techniques. A resist for KrF,for example, is used as the resist film 63. Next, by ordinarylithography techniques, the resist film 63 is left over only theamplifying transistor 24, and the resist film 63 over other parts isremoved.

When a positive type resist is used as the resist film 61 describedearlier, using a negative type resist as the resist film 63 makes itpossible to expose both the resists to light by one mask, and thusreduce the number of masks. When conversely a negative type resist isused as the resist film 61 described earlier, using a positive typeresist as the resist film 63 similarly makes it possible to reduce thenumber of masks.

Next, as shown in FIG. 7H, with the resist film 63 (see FIG. 7G) as anetching mask, the compressive stress film 54 is left on the amplifyingtransistor 24, and the compressive stress film 54 over other parts isremoved. This etching is performed by reactive ion etching (RIE) usingfor example a fluorocarbon (CF) base gas as an etching gas.

Thereafter the resist film 63 is removed. The drawing shows a stateafter the resist film 63 is removed.

The etching stopper film 52 and the compressive stress film 54 aredesirably of different film species because different film species makeit easy to secure a processing (etching) selectivity. For example, asdescribed above, the etching stopper film 52 is formed by a siliconnitride film, and the compressive stress film 54 is formed by a siliconoxide film. Of course, it may be vice versa, or two species of a siliconnitride film, a silicon oxide film, and a silicon oxynitride film can beselected and used.

The compressive stress film 54 can be formed under the followingconditions.

As an example, when a parallel plate plasma CVD (Chemical VaporDeposition) system is used to form a silicon oxide film, TEOS (TetraEthyl Ortho Silicate) and oxygen (O₂) are used as material gas, andhelium (He) is used as carrier gas. Suppose that as an example, flowrates of the respective gases are TEOS:O₂:He=2000 cm³/min:20000cm³/min:2000 cm³/min. In addition, conditions where plasma generationpower is 1500 W, the pressure of a film formation atmosphere is 1.07kPa, and the temperature of the substrate is 400° C. were applied. Thesilicon oxide film formed under such conditions had a compressive stressof 0.5 GPa.

As another example, when a parallel plate plasma CVD system is used toform a silicon nitride film, monosilane (SiH₄) and nitrogen (N₂) areused as material gas. Suppose that as an example, flow rates of therespective gases are SiH₄:N₂=100 cm³/min:4000 cm³/min. In addition,conditions where plasma generation power is 500 W, the pressure of afilm formation atmosphere is 400 Pa, and the temperature of thesubstrate is 400° C. were applied. The silicon nitride film formed undersuch conditions had a compressive stress of 1 GPa.

In addition, by changing these conditions as appropriate, thecompressive stress film of a silicon oxide film or a silicon nitridefilm having a desired compressive stress value can be formed.

Alternatively, when the etching stopper film 52 and the compressivestress film 54 are of a same species, a structure having an intermediatefilm of a different species inserted between the etching stopper film 52and the compressive stress film 54 is desirable.

Though not shown, for example, when a silicon nitride film is applied asthe etching stopper film 52, a silicon oxide film is laminated as theintermediate film, and thereafter an opening 53 is formed in the etchingstopper film 52 and the intermediate film over the amplifying transistor24 by lithography and reactive ion etching (RIE).

Thereafter the compressive stress film 54 is formed. Next the resistfilm 63 covering only the top of the amplifying transistor 24 is formed.With the resist film 63 used as an etching mask, etching leaves thecompressive stress film 54 on the amplifying transistor 24 and removesthe compressive stress film 54 over other parts. In this etching, aselective etching ratio of the silicon oxide film to the intermediatefilm can be secured, and thus stable etching treatment can be performed.

In addition, even when the films are of a same species, etching can beperformed by specifying time to control damage to the foundation filmand an amount of digging.

Next, a wiring process is performed. For example, wiring 71 forconnecting the gate electrode 32T of the transfer transistor 22 and adriving circuit (not shown) to each other, wiring 72 for connecting thegate electrode 32R of the reset transistor 23 and the driving circuit(not shown) to each other, wiring 73 for connecting the gate electrode32A of the amplifying transistor 24 and the floating diffusion 26 toeach other, wiring 74 for connecting the gate electrode 32S of theselecting transistor 25 and the driving circuit (not shown) to eachother, wiring 75 for connecting the diffusion layer 37 of the selectingtransistor 25 and a horizontal scanning circuit (output) (not shown) toeach other, wiring 76 for connecting the diffusion layer 35 sharedbetween the reset transistor 23 and the amplifying transistor 24 and thepixel power supply Vdd (not shown) to each other, and the like areformed.

The formation of each of the pieces of wiring 71 to 76 and the likedescribed above is similar to ordinary wiring formation.

For example, as shown in FIG. 7I, an interlayer insulating film 81 andcontact parts 73C for connecting the floating diffusion 26 and the gateelectrode 32A of the amplifying transistor 24 to each other, forexample, are formed. The contact parts 73C are formed by an ordinarytungsten plug. For example, contact parts (not shown) connected to theother gate electrodes 32, the diffusion layers 34 to 37, and the likecan also be formed at the same time.

Further, the wiring 73 is formed by making connection wiring 73P forconnecting the contact parts 73C to each other, and other wiring (notshown) is also formed at the same time. Further, a plurality of layersof an interlayer insulating film 82, upper layer wiring 77, aplanarizing insulating film 83, a color filter layer 84, a microchiplens 85, and the like are formed, whereby the solid-state image pickupdevice (CMOS image sensor) 1 is completed.

In the method of manufacturing the solid-state image pickup device 1according to the present embodiment, the compressive stress film 54having a compressive stress is formed on the amplifying transistor 24.Therefore, a local tensile stress applied to a channel region of theamplifying transistor 24 is relieved by the compressive stress of thecompressive stress film 54, so that an increase in variation in 1/fnoise of the amplifying transistor 24 can be suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

An embodiment (second embodiment) of a method of manufacturing asolid-state image pickup device according to the present invention willnext be described with reference to manufacturing process sectionalviews of FIGS. 8A and 8B.

In the foregoing first embodiment, the etching stopper film is formed toprevent excessive etching into the diffusion layers when a contact isformed. When the etching stopper film is not required, however, acompressive stress film may be formed without the etching stopper filmbeing formed.

A manufacturing method in this case (second embodiment) will bedescribed in the following.

As shown in FIG. 8A, as described with reference to FIGS. 7A to 7D, in asemiconductor substrate 11 of a first conduction type, a well region 12of a second conduction type is formed, the second conduction type beingan opposite conduction type from the first conduction type. Descriptionin the following will be made supposing that, as an example, the firstconduction type is an N-type and the second conduction type is a P-type.For example, an N-type silicon substrate is used as the above-describedsemiconductor substrate 11.

Next, a photodiode (PD) 21 for performing photoelectric conversion isformed at a predetermined position on the surface side of thesemiconductor substrate 11. The photodiode 21 is for example formed by aP-type region, an N-type region, and a P-type region from a bottom layerby performing ion implantation of phosphorus (P) as an N-type impurityand boron (B) as a P-type impurity using an ion implantation mask formedby patterning a resist film formed on the semiconductor substrate 11.The energy of the ion implantation is adjusted such that the photodiode21 is desirably formed between the surface of the semiconductorsubstrate 11 and a depth of 5 μm to 15 μm for visible light, and is forexample formed between the surface of the semiconductor substrate 11 anda depth of about 5 μm.

As described above, an N-type silicon substrate is used as thesemiconductor substrate 11, and therefore element isolation for thephotodiode 21 is performed by the well region 12.

Next, MOS type transistors within a pixel are formed.

A gate insulating film 31 is formed on the semiconductor substrate 11,and then gate electrodes 32 are formed. These gate electrodes 32 are thegate electrode 32 (32R) of a reset transistor of a pixel transistorgroup, the gate electrode 32 (32A) of an amplifying transistor of thepixel transistor group, and the gate electrode 32 (32S) of a selectingtransistor of the pixel transistor group.

In addition, the gate electrode 32 (32T) of a transfer transistor 22 isformed at the same time.

Next, side walls 33 are formed on the side part of each of the gateelectrodes 32 for a purpose of suppressing a short channel effect of aperipheral circuit, the pixel transistors and the like. The side walls33 are formed by a silicon oxide film, for example. Alternatively, theside walls 33 can be formed by a silicon nitride film.

Next, a resist mask (not shown) is formed by ordinary resist coating andlithography techniques, and diffusion layers 34, 35, 36, and 37 servingas sources and drains of the transistors are formed by ion implantationusing the resist mask. In this case, as an example, the diffusion layer35 is shared as one diffusion layer 35 of the reset transistor 23 andone diffusion layer 35 of the amplifying transistor 24, and thediffusion layer 36 is shared as another diffusion layer 36 of theamplifying transistor 24 and one diffusion layer 36 of the selectingtransistor 25.

In general, when holes and electrons are compared with each other ascarriers, holes are more easily trapped on the gate insulating film 31and the interface. Thus, in this case, electrons are selected ascarriers, that is, NMOS transistors are formed. A floating diffusion(FD) 26 is also formed in the semiconductor substrate 11 at the sametime by the ion implantation.

Thereafter, the resist mask used as mask for the ion implantation isremoved.

Next, silicide layers 41 to 44, 45, and 46 to 49 are formed on thediffusion layers 34 to 37, on the floating diffusion 26, and on the gateelectrodes 32, respectively, by a salicide process.

Prior to the salicide process, because silicide layers have low opticaltransparency, a silicide blocking film 51 is formed on the photodiode 21to prevent the formation of a silicide layer on the photodiode 21. Thesilicide blocking film 51 is desirably formed by a silicon oxide film, asilicon nitride film, a silicon oxynitride film or the like. A titaniumsilicide, a tantalum silicide, a molybdenum silicide, a nickel silicide,a tungsten silicide, a nickel-platinum silicide or the like can beapplied as the silicide layers 41 to 49.

Next, a compressive stress film 54 having a compressive stress is formedon an entire surface over the semiconductor substrate 11 so as to coverthe top of the amplifying transistor 24. This compressive stress film 54is formed by a silicon nitride film or a silicon oxide film, forexample.

Next, a resist film 63 is formed on the compressive stress film 54 byordinary resist coating techniques. A resist for KrF, for example, isused as the resist film 63. Next, by ordinary lithography techniques,the resist film 63 is left over only the amplifying transistor 24, andthe resist film 63 over other parts is removed.

Next, as shown in FIG. 8B, with the resist film 63 (see FIG. 8A) as anetching mask, the compressive stress film 54 is left on the amplifyingtransistor 24, and the compressive stress film 54 over other parts isremoved. This etching is performed by reactive ion etching (RIE) usingfor example a fluorocarbon (CF) base gas as an etching gas.

Thereafter the resist film 63 is removed. The drawing shows a stateafter the resist film 63 is removed.

The compressive stress film 54 can be formed under the followingconditions.

As an example, when a parallel plate plasma CVD system is used to form asilicon oxide film, TEOS (Tetra Ethyl Ortho Silicate) and oxygen (O₂)are used as material gas, and helium (He) is used as carrier gas.Suppose that as an example, flow rates of the respective gases areTEOS:O₂:He=2000 cm³/min:20000 cm³/min:2000 cm³/min. In addition,conditions where plasma generation power is 1500 W, the pressure of afilm formation atmosphere is 1.07 kPa, and the temperature of thesubstrate is 400° C. were applied. The silicon oxide film formed undersuch conditions had a compressive stress of 0.5 GPa.

As another example, when a parallel plate plasma CVD system is used toform a silicon nitride film, monosilane (SiH₄) and nitrogen (N₂) areused as material gas. Suppose that as an example, flow rates of therespective gases are SiH₄:N₂=100 cm³/min:4000 cm³/min. In addition,conditions where plasma generation power is 500 W, the pressure of afilm formation atmosphere is 400 Pa, and the temperature of thesubstrate is 400° C. were applied. The silicon nitride film formed undersuch conditions had a compressive stress of 1 GPa.

In addition, by changing these conditions as appropriate, thecompressive stress film of a silicon oxide film or a silicon nitridefilm having a desired compressive stress value can be formed.

Next, as described above with reference to FIG. 7H, a wiring process isperformed. For example, wiring 71 for connecting the gate electrode 32Tof the transfer transistor 22 and a driving circuit (not shown) to eachother, wiring 72 for connecting the gate electrode 32R of the resettransistor 23 and the driving circuit (not shown) to each other, wiring73 for connecting the gate electrode 32A of the amplifying transistor 24and the floating diffusion 26 to each other, wiring 74 for connectingthe gate electrode 32S of the selecting transistor 25 and the drivingcircuit (not shown) to each other, wiring 75 for connecting thediffusion layer 37 of the selecting transistor 25 and a horizontalscanning circuit (output) (not shown) to each other, wiring 76 forconnecting the diffusion layer 35 shared between the reset transistor 23and the amplifying transistor 24 and the pixel power supply Vdd (notshown) to each other, and the like are formed.

The formation of each of the pieces of wiring 71 to 76 and the likedescribed above is similar to ordinary wiring formation.

Thus, the solid-state image pickup device (CMOS image sensor) 2 iscompleted.

In the method of manufacturing the solid-state image pickup device 2according to the present embodiment, the compressive stress film 54having a compressive stress is formed on the amplifying transistor 24.Therefore, a local tensile stress applied to a channel region of theamplifying transistor 24 is relieved by the compressive stress of thecompressive stress film 54, so that an increase in variation in 1/fnoise of the amplifying transistor 24 can be suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

There is another advantage of being able to reduce each of the numbersof film formation steps, lithography steps, and etching steps, forexample, by one as compared with the manufacturing method according tothe first embodiment.

Another manufacturing method (third embodiment) in which the compressivestress film 54 having a compressive stress is formed on the amplifyingtransistor 24 will next be described with reference to a manufacturingprocess sectional view of FIG. 9.

As shown in FIG. 9, as described above with reference to FIGS. 7A to 7E,an etching stopper film 52 to cover gate electrodes 32 and the like isformed by a silicon nitride film, for example, on a semiconductorsubstrate 11.

Thereafter, only the etching stopper film 52 on an amplifying transistor24 is locally subjected to electron beam cure. This process increasesfilm density of the region of the etching stopper film 52 which regionis irradiated with an electron beam, so that only the etching stopperfilm 52 on the amplifying transistor 24 can be made to be a compressivestress film 54 having a compressive stress.

For example, irradiation was performed for five minutes with a pressureof 0.93 kPa in an atmosphere of the electron beam irradiation and with acurrent of 1 mA and an acceleration voltage of 10 keV as conditions forthe electron beam irradiation. The conditions are an example, and theelectron beam irradiation conditions can be changed as appropriatedepending on film density, film thickness and the like at the time offormation of the etching stopper film 52.

When a silicon nitride film is irradiated with an electron beam asdescribed above, silicon-hydrogen bonds (Si—H bonds) in the siliconnitride film are broken, and there occur excess silicon bonds. At thistime, excess bonds of nitrogen in the film are bonded to the siliconbonds to form stronger silicon-nitrogen bonds (Si—N bonds) than thesilicon-hydrogen bonds. Thereby the silicon nitride film is densified.In general, densifying the silicon nitride film increases compressivestress in the film.

Thereafter, as described above with reference to FIG. 7H and FIG. 7I,processes for the formation of an interlayer insulating film, theformation of wiring and the like, the formation of a planarizing film,the formation of a color filter, the formation of a condensing lens, andthe like are performed.

In the case of the manufacturing method according to the thirdembodiment, as in the manufacturing method according to the firstembodiment, the compressive stress film 54 having a compressive stressis formed on the amplifying transistor 24. Therefore, a local tensilestress applied to a channel region of the amplifying transistor 24 isrelieved by the compressive stress of the compressive stress film 54, sothat an increase in variation in 1/f noise of the amplifying transistor24 can be suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

Further, the compressive stress film 54 can also be made to function asan etching stopper film. Therefore the compressive stress film 54 canfunction as an etching stopper for preventing excessive etching of thesilicide layer 48 as a foundation when a connecting hole for connectinga contact part as a part of wiring connected to the floating diffusion26, for example, is formed in a part above the gate electrode 32A of theamplifying transistor 24.

Another manufacturing method (fourth embodiment) in which thecompressive stress film 54 having a compressive stress is formed on theamplifying transistor 24 will next be described with reference to amanufacturing process sectional view of FIG. 10.

As shown in FIG. 10, as described above with reference to FIGS. 7A to7E, an etching stopper film 52 to cover gate electrodes 32 and the likeis formed by a silicon nitride film, for example, on a semiconductorsubstrate 11.

Next, a resist film 65 is formed on the etching stopper film 52 byordinary resist coating techniques. A resist for KrF, for example, isused as the resist film 65. Next, the resist film 65 over the amplifyingtransistor 24 is removed to form an opening 66 by ordinary lithographytechniques.

Next, nitrogen ions are implanted into the etching stopper film 52 onthe amplifying transistor 24 with the resist film 65 used as an ionimplantation mask.

As a result, the etching stopper film 52 on the amplifying transistor 24is densified and increased in film density, so that the etching stopperfilm 52 on only the amplifying transistor 24 can be made to be acompressive stress film 54 having a compressive stress.

As conditions for the ion implantation, nitrogen ions were used as anion species, a dose thereof was set to 5×10¹⁴, and acceleration energywas set to 5 keV. The conditions are an example, and the ionimplantation conditions can be changed as appropriate depending on filmdensity, film thickness and the like at the time of formation of theetching stopper film 52.

Thereafter the resist film 65 is removed. Then a rapid heating process(RTA process) was performed to form Si—N bonds, whereby film density wasincreased. Conditions for the thermal process at this time were 850° C.and 20 s as an example. The thermal process conditions can be changed asappropriate in a range in which film density can be increased by formingSi—N bonds.

When nitrogen ions are implanted into a silicon nitride film asdescribed above, silicon-hydrogen bonds (Si—H bonds) in the siliconnitride film are broken, and there occur excess silicon bonds. Then, bythe thermal process, bonds of ion-implanted nitrogen are bonded to thesilicon bonds to form stronger silicon-nitrogen bonds (Si—N bonds) thanthe silicon-hydrogen bonds. Thereby the silicon nitride film isdensified. In general, densifying the silicon nitride film increasescompressive stress in the film.

Thus, it is desirable to introduce sufficient nitrogen so that the Si—Hgroups in the etching stopper film 52 are changed to Si—N bonds.

In the case of the manufacturing method according to the fourthembodiment, as in the manufacturing method according to the firstembodiment, the compressive stress film 54 having a compressive stressis formed on the amplifying transistor 24. Therefore, a local tensilestress applied to a channel region of the amplifying transistor 24 isrelieved by the compressive stress of the compressive stress film 54, sothat an increase in variation in 1/f noise of the amplifying transistor24 can be suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

Further, the compressive stress film 54 can also be made to function asan etching stopper film. Therefore, the compressive stress film 54 canfunction as an etching stopper for preventing excessive etching of thesilicide layer 48 as a foundation when a connecting hole for connectinga contact part as a part of wiring connected to the floating diffusion26, for example, is formed in a part above the gate electrode 32A of theamplifying transistor 24.

Another manufacturing method (fifth embodiment) in which the side walls33 formed on the side walls of the gate electrodes in the first tofourth embodiments are formed by a compressive stress film having acompressive stress will next be described with reference to amanufacturing process sectional view of FIG. 11.

As shown in FIG. 11, as described above with reference to FIGS. 7A to7C, side walls 33 are formed on side walls of each gate electrode on asemiconductor substrate 11.

At this time, for example, a silicon nitride film for forming the sidewalls covering the gate electrodes 32 is formed, and then the siliconnitride film in a region where an amplifying transistor 24 is formed isirradiated with an electron beam. Thereby the silicon nitride film of apart irradiated with the electron beam is densified to become acompressive stress film having a compressive stress.

Alternatively, after a silicon nitride film for forming the side wallscovering the gate electrodes 32 is formed, a resist mask (not shown)having an opening above the amplifying transistor 24 is formed, andnitrogen ions are implanted into the silicon nitride film on the regionwhere the amplifying transistor 24 is formed. Thereby the siliconnitride film of a part into which the nitrogen ions are implanted isdensified to become a compressive stress film having a compressivestress.

Reasons for an effect of densification of the silicon nitride film aresimilar to those of densification of the silicon nitride film in thethird embodiment and the fourth embodiment.

Thereafter the silicon nitride film for forming the side walls issubjected to whole-surface etching back to form the side walls 33 on theside walls of each gate electrode. In this case, the side walls 33 (33A)formed on the side walls of the gate electrodes 32 (32A) of theamplifying transistor 24 are a film having a compressive stress.

A process after the formation of the side walls 33 is similar to aprocess after the formation of the side walls 33 in the manufacturingmethods according to the first to fourth embodiments. Thus, though notshown, the compressive stress film 54 having a compressive stress isformed on the amplifying transistor 24 as in the manufacturing methodsaccording to the first to fourth embodiments.

In the case of the manufacturing method according to the fifthembodiment, as in the manufacturing methods according to the first tofourth embodiments, the compressive stress film 54 having a compressivestress is formed on the amplifying transistor 24. Therefore, a localtensile stress applied to a channel region of the amplifying transistor24 is relieved by the compressive stress of the compressive stress film54, so that an increase in variation in 1/f noise of the amplifyingtransistor 24 can be suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

Further, because the side walls 33A of the amplifying transistor 24 alsohave a compressive stress, a greater compressive stress can be appliedto the channel region. Therefore, an increase in variation in 1/f noiseof the amplifying transistor 24 can be suppressed more.

Next, there is a case of forming an element isolation region of an STI(Shallow Trench Isolation) structure next to the amplifying transistor24 in the first to fifth embodiments. This manufacturing method (sixthembodiment) will be described with reference to manufacturing processsectional views of FIGS. 12A to 12E.

As shown in FIG. 12A, as described above with reference to FIGS. 7A to7C, as in the first to fifth embodiments, a well region 12 is formed ina semiconductor substrate 11. Thereafter a silicon oxide film, forexample, is formed as a sacrifice oxide film 91 on the semiconductorsubstrate 11, and then a silicon nitride film 92 is formed.

Next, the silicon nitride film 92 and the sacrifice oxide film 91 on aregion for forming the element isolation region of the STI structure areremoved to form an opening 93 by ordinary lithography techniques andetching techniques.

Next, as shown in FIG. 12B, the semiconductor substrate 11 is etchedwith the silicon nitride film 92 used as an etching mask to form anelement isolation groove 94. This element isolation groove 94 forexample isolates regions for forming pixel transistors such as a regionfor forming a reset transistor, a region for forming a selectingtransistor, and a region for forming an amplifying transistor from forexample a region for forming a photodiode and a transfer transistor anda region (not shown) for forming a peripheral circuit.

In this case, a manufacturing method for a constitution provided withthe selecting transistor between a pixel power supply Vdd and onediffusion layer of the amplifying transistor in the first to fifthembodiments will be described as an example. Therefore, the amplifyingtransistor is formed at an end of the regions for forming the pixeltransistors.

Next, an insulating film 95 is formed on the silicon nitride film 92 soas to fill in the element isolation groove 94. The insulating film 95 isformed by a silicon oxide film, for example. In addition, before fillingthe insulating film 95, a silicon oxide film (not shown) may be formedby oxidizing the inside of the element isolation groove 94 by a thermaloxidation method, for example.

Next, as shown in FIG. 12C, the insulating film 95 is polished andremoved by chemical mechanical polishing (CMP) until the silicon nitridefilm 92 is exposed. At this time, the silicon nitride film 92 serves asa polishing stopper. As a result, an element isolation region 96 of theSTI structure made of the insulating film 95 is formed inside theelement isolation groove 94.

Thereafter, the silicon nitride film 92 is removed by wet etching usinga hot phosphoric acid. Further, the sacrifice oxide film 91 is removedby hydrofluoric acid or the like. As a result, as shown in FIG. 12D, theelement isolation region 96 of the STI structure is formed in thesemiconductor substrate 11.

Thereafter a process similar to that of the first to fifth embodimentsis performed. Incidentally, in the present embodiment, the selectingtransistor is formed between the pixel power supply Vdd and onediffusion layer of the amplifying transistor in the first to fifthembodiments. In the following, a case where the element isolation region96 according to the present embodiment is applied to the constitution ofthe first embodiment will be described as an example.

As a result, as shown in FIG. 12E, a photodiode 21, a reset transistor23, an amplifying transistor 24, a selecting transistor 25, a floatingdiffusion 26 and the like are formed in the semiconductor substrate 11.In this case, one diffusion layer 39 of the amplifying transistor 24 isdisposed and formed so as to be adjacent to the element isolation region96 of the STI structure.

Then, an etching stopper film 52 is formed so as to cover the photodiode21, the reset transistor 23, the selecting transistor 25, the floatingdiffusion 26 and the like, and a compressive stress film 54 having acompressive stress is formed so as to cover the amplifying transistor24.

In the above-described sixth embodiment, the well region 12 may beformed after the element isolation region 96 of the STI structure isformed in the semiconductor substrate 11, and thereafter the photodiode21, the reset transistor 23, the amplifying transistor 24, the selectingtransistor 25, the floating diffusion 26 and the like may be formed by aprocess similar to the above-described process. Alternatively, theelement isolation region 96 of the STI structure may be formed after thewell region 12 is formed in the semiconductor substrate 11, andthereafter the photodiode 21, the reset transistor 23, the amplifyingtransistor 24, the selecting transistor 25, the floating diffusion 26and the like may be formed by a process similar to the above-describedprocess.

In the case of the manufacturing method according to the sixthembodiment, as in the manufacturing methods according to the first tofifth embodiments, the compressive stress film 54 having a compressivestress is formed on the amplifying transistor 24. Therefore, a localtensile stress applied to a channel region of the amplifying transistor24 which stress is caused by silicide layers 101 and 102 formed on thediffusion layers 38 and 39 of the amplifying transistor 24 and theelement isolation region 96 is relieved by the compressive stress of thecompressive stress film 54, so that an increase in variation in 1/fnoise of the amplifying transistor 24 can be suppressed.

Thus, because lowering of an SN ratio can be suppressed, there is anadvantage of being able to obtain excellent image quality by achieving ahigh SN ratio.

While the above description has been made of a CMOS sensor of aso-called front-surface irradiation type, a compressive stress filmaccording to an embodiment of the present invention is similarlyapplicable to an amplifying transistor in a CMOS sensor of aback-surface irradiation type shown in FIG. 13, for example.

As shown in FIG. 13, a plurality of pixel sections 121 having forexample a pixel transistor group 123 (a part thereof is shown in thedrawing) of an photoelectric conversion section (for example aphotodiode) 122 for converting incident light into an electric signal, atransfer transistor, a reset transistor, an amplifying transistor, aselecting transistor and the like are formed in an active layer 112formed by a semiconductor substrate 111. A silicon substrate, forexample, is used as the semiconductor substrate 111. Further, a signalprocessing section (not shown) for processing a signal charge read fromeach photoelectric conversion section 122 is formed.

An element isolation region 124 is formed in a part of the periphery ofthe pixel sections 121, for example between pixel sections 121 in a rowdirection or a column direction, for example.

In addition, a wiring layer 131 is formed on the front surface side ofthe semiconductor substrate 111 (lower side of the semiconductorsubstrate 111 in the drawing) where the photoelectric conversionsections 122 are formed. The wiring layer 131 is composed of wiring 132and an insulating film 133 covering the wiring 132. A supportingsubstrate 135 is formed on the wiring layer 131. The supportingsubstrate 135 is formed by a silicon substrate, for example.

Further, in a solid-state image pickup device 6 of FIG. 13, aplanarizing film 141 having an optical transparency is formed on theback surface side of the semiconductor substrate 111. A color filterlayer 142 is formed on the planarizing film 141 (upper surface side inthe drawing). In addition, a condensing lens 151 for condensing incidentlight on each photoelectric conversion section 122 is formed on thecolor filter layer 142.

A compressive stress film according to an embodiment of the presentinvention can be applied on the amplifying transistor of the pixeltransistor group 123.

Also in the CMOS image sensor of the back-surface irradiation type, 1/fnoise is suppressed by applying a compressive stress film according toan embodiment of the present invention to a constitution in whichtensile stress is applied to a channel region of the amplifyingtransistor formed by an NMOS transistor.

As described above, in the embodiments of the present invention, thecompressive stress film 54 on the amplifying transistor 24 is formed sothat compressive stress is applied to the channel region of theamplifying transistor 24 in the pixel transistor group of the CMOS typeimage sensor. Generally, tensile stress is applied to an NMOS transistorin order to increase mobility of a channel region of the NMOStransistor. However, the embodiments of the present invention preventslowering of an SN ratio by suppressing an increase in variation in 1/fnoise of the amplifying transistor 24, and makes it possible to obtainexcellent image quality by achieving a high SN ratio. In addition, inthe embodiments, the compressive stress film 54 is formed only on theamplifying transistor 24, and therefore the mobility of othertransistors is not degraded.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An imaging device comprising: a photoelectricconversion section; a transfer transistor coupled to the photoelectricconversion section; a floating diffusion coupled to the transfertransistor; an amplification transistor coupled to the floatingdiffusion and having a gate region; and a wiring coupled to the gateregion, wherein the gate region includes a gate terminal and a silicidelayer, the silicide layer is disposed at an upper side of the gateterminal, a first film is disposed at the side of the gate terminal in across-section view, a second film is disposed over the gate terminal andfirst film, the first film is selected from an oxide film and a nitridefilm, and the second film is selected from an oxide film, a nitride filmand an oxynitride film.
 2. The imaging device according to claim 1,wherein the second film includes a compressive stress film.
 3. Theimaging device according to claim 1, further comprising: a resettransistor coupled to the floating diffusion.
 4. The imaging deviceaccording to claim 3, further comprising: a pixel power source coupledto the reset transistor and the amplification transistor.
 5. The imagingdevice according to claim 4, further comprising: a selection transistorcoupled to the amplification transistor.
 6. The imaging device accordingto claim 5, further comprising: a constant-current source coupled to theselection transistor.
 7. The imaging device according to claim 5,further comprising: an etching stopper film disposed over at least oneof the reset transistor, the amplification transistor and the selectiontransistor.
 8. The imaging device according to claim 1, wherein theimaging device is a backside illuminated sensor.
 9. The imaging deviceaccording to claim 1, further comprising: a semiconductor substrateconfigured to have a first side as a light incident side and a secondside opposite to the first side; and a silicide blocking layer disposedat the first side of the semiconductor substrate, wherein, thephotoelectric conversion section is disposed in the semiconductorsubstrate.
 10. The imaging device according to claim 9, wherein thesilicide blocking layer is selected from the group consisting of asilicon oxide film, a silicon nitride film and a silicon oxynitridefilm.
 11. The imaging device according to claim 9, further comprising: agate insulating film disposed between the first side of thesemiconductor substrate and the gate terminal in the cross-section view.12. The imaging device according to claim 9, further comprising: awiring layer disposed at the second side of the semiconductor substrate;a micro-chip lens disposed at the first side of the semiconductorsubstrate; and a color filter layer disposed between the semiconductorsubstrate and the micro-chip lens.
 13. The imaging device according toclaim 1, wherein the gate terminal includes polysilicon.
 14. The imagingdevice according to claim 1, further comprising: an isolation regiondisposed adjacent to the amplification transistor.
 15. The imagingdevice according to claim 14, wherein the isolation region includes ashallow trench isolation structure.
 16. The imaging device according toclaim 1, further comprising: a signal processing circuit coupled to theamplification transistor, wherein, the signal processing circuit isconfigured to output an amplified signal based on a signal charge fromthe photoelectric conversion section.
 17. The imaging device accordingto claim 1, wherein the silicide layer is selected from the groupconsisting of a titanium silicide, a tantalum silicide, a molybdenumsilicide, a nickel silicide, a tungsten silicide and a nickel-platinumsilicide.